The present applicant manufactures a device for catching, fixing and removing foreign objects form the body of a human patient. These foreign objects can include stones, fragments and concrements in the medical fields of urology and gastro-enterology. In the present device, both ends of a number of individual wires are held together by a ring. Normally, the wires have a circular cross-section. One of these rings forms the distal end of a shaft and the other ring is spaced distally axially from the first ring. When the individual wires are all bowed radially outwardly and are distributed at regular intervals around the circumference of the axis, then these wires form longitudinal strands of an envelope defining a cavity centered on the long axis of the shaft. The wires are resilient and are given an outwardly bowed symmetrically or helically twisted shape so as to define a basket cavity radially inwardly of the envelope defined by the wires. The number of wires is usually in a range of from two to six. The entire device is placed within a sheath. For catching the foreign object, the distal end of the shaft and basket assembly is advanced out of the distal end of the sheath, allowing the resilience of the wires to form the basket by outward bowing. Once the foreign object is fished into the basket, then the shaft can be withdrawn proximally, to a greater or lesser extent, in order that the distal end of the sheath should squeeze down the diameter of the basket so that the basket wires grip the foreign object in the reduced diameter basket cavity immediately adjacent the distal end of the sleeve. Then the shaft and sleeve can together be withdrawn in the proximal direction to carry the foreign object in the basket out of the body.
In endoscopic surgery, a small diameter of the sheath is desirable. Currently the devices on the market have a sheath diameter falling within a range of outside diameters from 0.63 to 1.83 mm, which corresponds to a range of 1.9 to 5.5 French (1 French=⅓ mm).
One disadvantage of the presently marketed devices is that soldered, welded or glued joints are used to fix the individual wires to the rings and to the shaft. These connections represent a potential failure risk and, in any event, their ultimate strength has to be ascertained by extensive examination and testing.
Apart from this, the jointing of the wires at the rings defines the greatest outer diameter of the shaft element of the device, which therefore determines the inner diameter of the sheath and therefore indirectly determines the outer diameter of the sheath, setting a limit on the minimization of the outer sheath diameter.
Furthermore, the envelope of wires determines a characteristic mesh size of the basket and this mesh size has to be suitable both for fishing an object into the basket and then for retaining it within the basket until it has been removed from the body. Whereas a small mesh helps retention and removal, it does not help in the process of fishing the foreign object into the basket. A compromise mesh size has to be adopted.
EP-A-818 180 discloses an endoscope accessory in the form of a tube with a slitted distal end portion. The slits can be deformed radially outwardly to define a plurality of openings, by pulling from the proximal end of the tube on a pull wire 13 connected at its distal end to the distal end of the slitted portion. The disclosure of EP-A-737 450 is, in these respects, similar and U.S. Pat. No. 4,807,627.
EP-A-512 729 discloses an endoscopic surgical instrument which includes a tube having a slitted portion at its distal end. In a relaxed disposition of the wall portions between the slits, they are spaced apart from one another to form a basket. The slitted tube is itself co-axially within an outer tube having a distal end, and the basket can be closed down by drawing the basket, beginning at its proximal end, proximally into the outer tube, past the distal end of the outer tube. The slitted tube is made of a polyurethane material and the basket is formed by the application of steam heating to the slitted end.
DE-A-197 22 429 discloses a Nitinol tube, slitted at its distal end, for use as a basket to gather stones from bodily cavities. It is said to differ from previous such baskets in that the strands of the basket are unitary with the tube.
WO 94/18888 is another disclosure of a stone-gathering basket made from a plurality of Nitinol wires. The wires are arranged around the circumference of the basket in pairs and given a helical twist, which is said to increase the number of points of contact between the basket and entrapped calculi and to require of the physician no more dexterity than the prior art baskets, having a smaller number of contact points, required.
WO 96/23446 discloses a stone-gathering basket in which a distal half of the basket envelope exhibits a greater number of basket strands than the proximal half of the basket envelope. Each lengthwise strand in the proximal half of the baskets splits at half distance over the basket envelope into a plurality of strands which help to define the proximal half of the basket envelope. At the distal end of the basket is a cap to which all of the filaments defining the basket envelope are welded.
WO 99/16365 discloses a stone-gathering basket defined by a plurality of legs and with discussion what cross-sectional shapes of the legs are useful, and what surface topography on the inward facing surface of each leg.
WO 99/48429 is another disclosure of a stone gathering basket made unitary from a tube with longitudinal slits at its distal end, the basket being relaxed in its expanded configuration and of a material which can be a nickel titanium shape memory alloy such as Nitinol.